African climate changes during C4 plant evolution and expansion

在这个工作包(TP 2)中，我们建议通过研究陆源植物脂肪生物标记物及其分子、碳、氢、同位素特征来建立非洲大陆植被变化的详细记录。这些分析将结合东赤道和南大西洋海洋沉积物岩心样品的花粉组合进行。在第一阶段(1-3年)，我们将重点放在中新世晚期，涵盖C4草原的大规模扩张。在第二阶段(4-6年)，我们将调查从始新世晚期到渐新世早期，C4植物进化的时间间隔。根据CO2-Treshold模型，C4植物的进化和扩张主要与大气中二氧化碳水平的下降有关。而对于始新世/渐新世，二氧化碳水平的下降被重建，中新世二氧化碳水平的估计与检测到的C4草原的扩张之间存在着不匹配。反过来，这种对比又表明了其他环境因素对大规模植被变化的重要性，例如降雨量和季节性。为了解决这一差异，我们将在陆地脂肪生物标志物上应用新的化合物特有的氢同位素分析，从而能够准确地评估大陆水文条件。将脂肪生物标记物与花粉记录进行详细比较，可以区分不同成分的C4植物。此外，我们将建立大西洋东南部过去海表面温度(SST)变化的有机地球化学记录，以揭示大陆环境变化和海洋变化之间的气候联系。在这方面，该TP获得的结果将直接与TP 4中生成的海洋代理数据相媲美。在整个研究单位内，该TP与TP 01一起提供陆地植被和气候参数的数据库，以定量验证所获得的全球碳和水循环模拟结果。

In this workpackage (TP 2) we propose to establish detailed records of vegetation changes on the African continent by investigating terrigenous plant lipid biomarkers and their molecular, carbon and hydrogen, isotopic signatures. These analyses will be conducted in combination with pollen associations on samples from marine sediment cores in the eastern equatorial and southern Atlantic. In the first phase (year 1-3) we focus on the middle to Late Miocene, covering the large-scale expansion of C4 grasslands. In the second phase (year 4-6) we will investigate the interval from the Late Eocene to the Early Oligocene, when C4 plants evolved. Both evolution and expansion of C4 plants have yet mainly been linked to decreasing atmospheric CO2 levels according to the CO2-treshold model. While for the Eocene/Oligocene interval falling C02 levels were reconstructed a mismatch exists between estimates of Miocene pCO2 levels and the detected expansion of C4 grasslands. This contrast, in turn, points to the significance of other environmental factors for large-scale vegetation changes, such as amount and seasonality of precipitation. In order to resolve this discrepancy, we will apply novel compound-specific hydrogen isotope analyses on terrestrial lipid biomarkers, which enable accurate assessment of continental hydrological conditions. A detailed comparison of lipid biomarker with pollen records will allow the distinction between C4 vegetations of different composition. In addition, we will establish organic-geochemical records of past sea-surface temperature (SST) changes in the south-eastern Atlantic to unravel climatic linkages between the continental environmental changes and oceanographic variations. In this respect, the results obtained by this TP will directly be comparable to the marine proxy data generated in TP 4. Within the entire Research Unit, this TP, in conjunction with TP 01, provides the data base of terrestrial vegetation and climate parameters to quantitatively validate the obtained modelling results on the global carbon and water cycle.